This invention relates generally to waveform to pulse conversion and more specifically to techniques for converting arbitrary analog waveforms to sequences of pulses.
Pulse generators are well known, for example, for DC controllers and other applications. However, the typical pulse generator is an adaptation of a conventional oscillator or monostable multivibrator, which can produce undesired or spurious transients when the pulse triggering is terminated. Such transients could be confused with trailing pulses, so that the counting of pulses is an inaccurate representation of the intended pulse count.
A typical pulse generator is responsive to a trigger related to a threshold level; that is, pulses are generated when a level input is applied that exceeds a predetermined threshold that has established a trigger point. The duration of the input above the threshold typically corresponds to the duration of the pulse train or oscillation period.
A classic van der Pol (vdP) oscillator is a simple nonlinear oscillator circuit and is a useful starting point for use as a pulse generator. However, the classic vdP oscillator is not readily controllable.
Circuitry is needed which is simple and yet which addresses needs in various applications. For example, in co-pending and co-owned U.S. application Ser.No. 09/429,527, a method and apparatus for generating pulses from analog waveforms are disclosed. The application discloses, in an embodiment of the invention, an analog waveform having two information regions used in a communication system. A first information region drives the operating point of the circuit to an unstable region to substantially instantly produce oscillations while a second information region will drive the operating point of the circuit out of the unstable region to stop the oscillations substantially instantaneously.
In a conventional communication system, however, various multilevel signaling schemes, such as QAM, are used to enhance the capacity of the information being transmitted through a given channel. Of course, this is done at the expenses of the noise performance of the communication system.
With the development of electronic technologies, it has now been determined that transmission of radio frequency signals at the frequency of modulation is both possible and practical over a broad spectrum, from subaudio frequencies to microwave frequencies. However, heretofore, there has not been a modulation and demodulation technology which takes advantage of this capability using multilevel signaling scheme.
It is desirable to have a pulse method and apparatus that addresses the foregoing needs.
According to the invention, a method and apparatus are provided for generating oscillations (groups of pulses) in response to input analog waveforms which involves exciting, with a known but arbitrary analog waveform, a circuit with a variable operating point and having a transfer function characterized by alternating unstable operating regions and stable operating regions. The circuit or device according to the invention is a form of oscillator having a multi-N-shaped or multi-S-shaped V-I profile that can be made to exhibit nonlinear operation; that is, to oscillate during excursion of current and voltage through one of the unstable operating regions.